There are several applications that require tubes to be made and used on site. One such application is casing boreholes, in particular in the oil industry; a second is making ducting of great length such as submarine pipelines, and finally another consists in restoring or lining buried pipelines or casing.
The purpose of a borehole, in particular an oil exploration borehole, is to establish a passage for communication between the surface and an objective underground. For most wells, the initial diameter of the bore is large, whereas once the well is completed, the final communication passage is of small diameter: usually less than 6" (152 mm). The passage is then of constant diameter equal to this small final diameter up the entire height of the well.
To establish such communication while withstanding the pressures encountered, longer and longer successive concentric lengths of casing are lowered and suspended from the surface and are then cemented in place. Given that each length of casing must pass through the preceding length, its outside diameter must be less than the inside diameter of the preceding length, and to obtain a final access diameter of 4" to 8" (102 mm to 203 mm), it is necessary to begin with a borehole of large diameter, in particular 171/2" (445 mm), and even 36" and 26" (915 mm and 660 ram) for offshore boreholes.
Present methods thus require an initial hole of large diameter to be drilled in order to have a sufficient number of lengths of casing available for making the well. The direct consequences of this technique are that the time required for drilling is long and consumables (steel tubes, drilling mud, sealing cement, etc . . . ) are needed in large quantities. In addition, because the initial lengths of casing are of large diameter, their wall thicknesses are limited for reasons of weight. The capacity of such initial lengths of casing to withstand high internal pressures is therefore limited. It is necessary for each following inner tube to be suspended from the surface in order to increase the ability of the top portion of the casing to withstand the high pressures that obtain at the bottom of the well.
In addition to the large quantity of consumables, and the long time required by said operations of drilling and installing concentric casing, present techniques suffer from other drawbacks. Cementing is difficult to perform because of the narrowness of the annular space and the hazards of the terrain drilled through. In addition, the fact that the casing is made of metal constitutes an obstacle to performing various measurements, in particular electrical measurements, that are required for locating productive layers for the future purpose of putting the hydrocarbon reserves into production.
There thus exists a need to simplify the operations of drilling and of casing.
In addition, it is difficult and lengthy to install pipework, in particular offshore and in particular when of relatively large diameter, because of the need for a plurality of lengths of steel tube that make up the pipework to be interconnected end-to-end, generally by welding, and for said pipework to be paid out progressively from the vessel on which it is assembled while it is being assembled and without kinking it, thereby giving rise to high tensions during laying. There is also a need to make the laying of such pipework easier, particularly in deep water and/or if the pipework is large in diameter.
Finally, restoring or lining underground casing or pipework implies that an inner lining must be installed in a faulty pipe (that has become porous or unsealed when lengths are connected together), said lining being capable, at least in some locations, of replacing the pipework itself which may have completely disappeared due to corrosion.
The present invention seeks to satisfy these needs by making it possible when applied to a borehole to retain a small drilling diameter over the entire length of the well together with small diameter casing. When applied to making offshore pipework, the invention enables the pipework to be installed while flat, thereby reducing the minimum acceptable radius of curvature during laying and consequently reducing tension during laying; and when applied to repairing faulty pipework, the function of the preform is to consolidate the pipework and sometimes even to take its place. These results are obtained by using a deformable and settable composite material of minimum radial size prior to setting and possessing a structure that enables it to be folded into its minimum-size state and to be radially inextensible even before setting so as to enable it to take up its final shape even in the absence of any outside restraint.